As display devices become more sophisticated, there are increasingly high demands for the oxide active layer. As a kind of active layer material, an oxide semiconductor has the advantages of high carrier mobility, low fabrication temperature, good uniformity in large area, high optical transmittance etc., in comparison with the traditional material of amorphous silicon (a-Si), and these advantages also makes the oxide thin film transistor (Oxide TFT) suitable for the preparations of high resolution TFT-LCD, AM-OLED, flexible display, transparent display and other new types of display devices.
However, the stability problem of the oxide TFT has always been the manufacturers' concern, especially the damage to the device when the oxide device is exposed to UV irradiation. From the perspective of material characteristics, the width of band gap of the oxide semiconductor generally ranges from 3.2 eV to 3.6 eV, which has good absorption on the short-wavelength UV rays. Therefore, under the light irradiation and the gate supplied with long-time negative bias voltage, the threshold of the oxide thin film transistor (e.g. IGZO TFT) will shift sharply in negative direction, which will cause device failure. Because the threshold will shift in different directions when the bias voltage, interface state or fabrication process is changed, it is difficult to maintain long-time stability of the thin film transistor under the light irradiation. At present, this phenomenon can only be quantitatively interpreted by a conventional principle of injecting or capturing photogenerated holes, the effect of which depends on different energy levels of the photogenerated carriers formed on the surface of the channel.